1. Field of the Invention
The invention relates to a method and a system which is used for detection of misalignment and for prediction of faults on rotating machines and their components by means of thermography.
2. Description of Related Art
Various methods are known for predicting faults on rotating machines and their components, such as bearings, and the alignment of motors. Simplest is visual inspection in which obvious damages are sought. These damages are the emergence of oil or lubricating grease or visible leaks. In visual inspection fill levels of storage tanks, but also the accumulation of material in filters are also monitored.
Vibration analysis was developed from acoustic inspections which are carried out in part with a stethoscope. In doing so, vibration signals are recorded with microphones or accelerometers. Mostly piezosensors which are also made as MEMS modules are used nowadays as accelerometers. A signal for vibration rate or displacement can be obtained from the acceleration signal of the accelerometer by single or double integration. Thus, the original frequency range of the acoustic inspections is expanded from what is audible to ultrasound. Moreover, mathematical and digital methods can be used by further electronic processing in the evaluation of the data of vibration measurement, such as, for example, Fourier analysis.
Another method is oil analysis. While this method is relatively revealing, it is associated with high cost because, on the one hand, an oil sample must be taken, and on the other, the samples must be sent to a laboratory; this entails great time expenditure.
Another method which is being increasingly used in practice is thermography. Here, a picture of a machine component of interest is taken with an infrared camera. Often, photographs in the visible spectral range are superimposed on these pictures; the photographs have been taken from a similar or the same perspective, for example, the infrared camera and the camera for the visible spectral range being integrated in a housing. Thus, U.S. Pat. No. 7,809,258 describes such a camera with a technique for superimposing pictures from the visible and infrared spectral range. The evaluation of the photographs is reserved to the human observer who is often limited to finding especially striking temperature values in the infrared picture. This method is helpful to quickly locate, for example, a bearing which has run hot or a clutch which has become hot due to misalignment, and to initiate corrective measures. This location-finding of components which have become hot, however, is only possible when a human observer correctly determines the component which has become hot in the infrared picture. Thus, U.S. Pat. No. 7,706,596 mentions (in column 5 in lines 54-60) that it is necessary that an observer must have certain skills for the evaluation of infrared pictures.
Approaches to machine evaluation of infrared pictures are described in U.S. Pat. No. 7,528,372. There, the superposition of infrared pictures and photographs in the visible spectral range is mentioned. A comparison of thermography photographs which is carried out with computers is, in general terms, described as a “thermal performance algorithm”. Little is given concerning the specific execution of these algorithms.
These algorithms can be applied to thermography photographs which have been taken at long time intervals, such as, for example, a picture of a new machine and a picture of the same machine after it has been in operation for a long period of time. Changing ambient conditions, such as the temperature in the factory hall in which the machine has been set up, engender problems in discovering these algorithms. Other problems are changes of operating conditions which are due to different operating states of the machine and also to the temperature of the medium to be conveyed changing in a pump which is driven by a motor, for example.
It is often possible to manage with artificially induced full load of a machine system which is to be assessed when the system has been subjected to initial start-up or maintenance and then to take a thermography picture. To check the machine at a later time, again full load is artificially produced and a thermography picture is taken. These two thermography pictures are then compared by experienced evaluators. This method is expensive and of little reliability due to the artificial inducement of the full load and the limited availability of experienced evaluators. It depends on the experience and ability of the evaluator whether and to what extent parameters, such as, for example, the ambient temperature or the amount and/or the temperature of a conveyed medium are correctly taken into account.